Copending application Ser. No. 318,481, filed Dec. 26, 1973, now U.S. Pat. No. 3,843,380 on a "Process for Spray Drying Pigment", assigned to assignees of the present application, describes a process for spray drying pigment particles, e.g., pigmentary titanium dioxide, in which a slurry of the pigment particles in water is prepared with about 0.1 to about 5% of a water-dispersible thickener, the thickener being defined as capable in small concentrations of less than about 5.0% of visibly thickening when added to water. Water soluble or water-dispersible organic colloidal high molecular weight thickeners are well known in the art. Particularly suitable thickeners for the invention of said co-pending application are water-soluble polymerized alkylene oxides, for instance ethylene oxide polymers described in prior U.S. Pat. Nos. 2,866,761, 2,914,491 and 2,917,470, marketed under the Union Carbide trademarks Polyox WSR N-10, molecular weight 100,000; and Polyox WSR N-80, molecular weight 200,000. Another class of thickeners which can be employed are the esters of polyalkylene glycol or glycerol and fatty acids such as water-dispersible glycerol esters of higher fatty acids such as stearic acid, e.g. Arlacel 165 (trademark Atlas-ICI) having an HLB value near 11. Other suitable thickeners such as the glycol esters of higher fatty acids, ethoxylated sterols, the ammonium salt of a partial ester of methylvinyl ether/maleic anhydride copolymer and ethoxylated lauryl alcohol, polyvinyl alcohol, alkylene metal caseinates, natural gums including gum tragacanth, locust bean gum, caraya gum, guar gum, polyacrylates, polyacrylamides and others are given in said co-pending application. Still another class of thickeners are the cellulosic-type thickeners such as hydroxy propylmethyl cellulose and hydroxy ethyl cellulose.
It was found that the addition of such thickeners to the pigment slurry prior to spray drying resulted in an efficient collection of fines producing an essentially dustless product in which there was little or no loss of pigment in cyclone separation following drying.
It was also found that the pigments prepared in accordance with the invention of the co-pending application could readily be bulk handled and bulk stored without caking and destroying their free-flowing properties.
The invention of the copending application is suitable for the preparation of pigments for plastic and also latex and solvent grade paints. The thickeners are employed in amounts of about 0.3% for paint pigment grades and of about 0.1% for plastic pigment grades. Up to 2.0% of the thickener can be employed however. A feature of the invention of the copending application is that the thickener should be soluble or the bonds formed thereof should be readily destructible in the paint or plastic system to which the pigment is added to render the pigment readily dispersible in such system.
The invention of the copending application is particularly applicable to the spray drying of titanium dioxide.
The disclosure of said copending application Ser. No. 318,481 is incorporated herein by reference.